Regex validating string parameters when using ``%`` formatting in python

Question

In python you can format parameters using %-formatting like that:

"Foo %(bar)" % {"bar": baz}

I use some parameters like %(name)s for string rendering in Python (I am coding an auto mail apps) and I dont know how to evaluate it before using because if the user input the wrong parameter such as %(names or %names or %name)s or %%name()s or something like that, the apps will comes to error.

So there are valid: %(foo), %(bar) but not %(foo)s, %(foo, %foo etc? — Bohemian
– Bohemian ♦, Commented Oct 21, 2014 at 4:11
Only string in form of %(something)s is valid. Note that something can contains "%(" or ")s" but not both — Phuc Tran
– Phuc Tran, Commented Oct 21, 2014 at 4:13

Bohemian · Accepted Answer · 2014-10-21 04:14:25Z

1

This regex matches the "correct" input, eg %(foo)s:

^%\(\w+\)s$

This allows any "word" char for the name. To restrict the "name" part to just lowercase letters (as your examples all are):

^%\([a-z]+\)s$

answered Oct 21, 2014 at 4:14

Bohemian♦

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4 Comments

smac89 Over a year ago

Op says the string in the middle can contain %( or )s but not both

Bohemian Over a year ago

@Smac89 I think English is not the OP's first language. Examples of bad input in question suggest this is what he wants.

Phuc Tran Over a year ago

@Bohemian: Smac89 is right. I also need to test that case. Sorry for not mentioning in the questions. Any suggestion?

Bohemian Over a year ago

But your comment says "Only string in form of %(something)s is valid". Please clarify what is valid and what is not valid by posting examples of each in your question.

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